Regolith Types Research Articles

Optimizing lunar regolith for vat polymerization and sintering: pre-processing & mineral composition impact

Lunar regolith is the most abundant resource on the lunar surface, which can be used for in-situ fabrication and repair technologies. Vat photopolymerization-based additive manufacturing is among the most promising techniques, capable of producing precise ceramic parts of complex shapes from the lunar regolith feedstock for the needs of future crewed exploration missions to the Moon. One of the under-studied aspects of additive manufacturing with lunar regolith is the pre-and post-treatment procedures, which would ensure optimal energy and material consumption and the best printing performance. The goal of the present article was to define the influence of the mineral composition of lunar regolith simulants and the parameters of their pre-processing on the properties of sintered regolith ceramics. It was found that the highland regolith could be sintered to higher relative density compared to the mare regolith. The optimal sintering temperature was determined to be 1150 °C for both types of lunar regolith. An optimal mineral and fractional composition for the regolith feedstock was determined based on the trade-off analysis between lunar regolith sinterability and its printability via vat photopolymerization-based additive manufacturing. Vat-polymerization was performed to produce complex-shaped ceramic parts, yielding 95 % of relative density and a mean ultimate flexural strength of 106 ± 5 MPa, confirming the proposed trade-off point.

Australian critical metal exploration for analogues of Chinese ionic-clay REE deposits

The clean energy transition has focused attention on the critical metals required for manufacture of new energy technologies. The extremely heterogeneous distribution of critical metal mineral deposits requires that countries must make new discoveries of key critical metals to avoid potential future geopolitical risks. Although Australia has REE resources, they are mainly of LREEs, so deposit styles with significant HREEs are key targets. The most obvious are the so-called ionic-clay REE deposits of southern China that are the major global suppliers of HREEs. Mineral exploration in Australia using the Chinese model is producing hitherto unrecognized REE concentrations, here termed regolith-hosted REE mineralization, in a variety of regolith types in several weathering environments, particularly in Western and South Australia. Amongst these has been the discovery of near-surface, regolith-hosted REE mineralization in the Albany-Fraser Orogen which has the potential to complement REE production from the giant Mount Weld carbonatite and other monazite-sand deposits in Western Australia. Widespread near-surface, regolith-hosted REE mineralization is present over an area of 12,000 km2 in the Esperance District. As much of this area is beneath barren Eocene-aged cover clays, all the new REE discoveries have been made, and are being delineated using shallow drilling, to depths of less than 80 m. The exploration implication is that the search space for regolith hosted REE deposits in Western Australia remains immature. These recently discovered deposits have both similarities and contrasts with geological features of ionic clay hosted REE deposits in China. Similarities include their apparent paragenesis and geometry, particularly their blanket morphology, sub-horizontal and gentle dips, and the common, but not exclusive, relationship with felsic basement terranes. However, Western Australian prospects are related to Upper Cretaceous to Eocene climates rather than more recent weathering under sub-tropical conditions. Whether the deposits can be developed to production remains unclear, with project economics tied closely to the efficacy of mineral processing technologies that target high REE extraction rates and recoveries.

Characterization of a Simulated Martian Regolith Ecosystem by Proton Nuclear Magnetic Resonance (NMR) Relaxometry and Fourier Transform Infrared (FT-IR) and Visible (VIS)-Near-Infrared (NIR) Spectroscopies

Of the various Martian soil simulant mixes developed by NASA and Jet Propulsion Laboratory (JPL), three types were chosen that have the closest features to those of the Martian regolith to be analyzed. The characterization of the Martian regolith types was performed the advanced methods of 1H nuclear magnetic resonance (NMR) relaxometry, Fourier transform infrared (FT-IR) spectroscopy and visible (VIS)-near-infrared (NIR) spectroscopy, as well as classical methods such as pH, the electrical conductivity, and the total dissolved solids. These analyses showed that trace water, nitrogen, phosphorus and potassium are present in the Martian regolith simulant. A Martian Garden has been built with the Martian soils, in which various vegetables have been seeded. Among the Fourier Transform infrared (FT-IR) spectra acquired for the plants, a high degree of similarity was observed, which indicates that the substrate ‘Martian regolith simulant of terrestrial soil’ does not significantly influence the structure of the radish, peas and bean leaves, stems, or roots. Nevertheless, the results of 1D 1H nuclear magnetic resonance (NMR) relaxometry indicate that the substrate presents a high influence on the water dynamics in plant pores at the level of roots, stems and leaves and in bound water. A Marsarium was designed and built, where all types of Martian and terrestrial soils were introduced, together with a family of ants. The ants adapted to the imposed conditions, as they dug tunnels in the soils.

Impact response of physical analog of Martian regolith

A careful examination of collisional processes occurring on surfaces of Solar System objects requires data on the dynamic properties of porous geological materials. Shock waves traveling in sand with physical properties analogous to those of some types of Martian regolith are studied in a series of uniaxial plate impact experiments. The initial density of the samples and average grain size are 1.30 g cm−3 and 95 μm, respectively. The obtained Hugoniot of this simulant is in general agreement with those of previously studied sands. The effect of porosity and grain morphology on Hugoniots of these geological materials is also highlighted. A laser velocimetry technique is used to observe the structure of propagated waves. Wave fronts with rise times on the order of several hundred or tens of microseconds were recorded in the pressure range of 0.5 to 1.7 GPa. For the simulant, a value of 1.91 was found for an exponent in the relationship between rise time and pressure τ∼p−m. Additionally, exponents for different granular and silica-rich systems studied earlier were also provided. An analysis of wave thickness revealed that in the pressure range of 0.5–1.1 GPa, this parameter can be associated with the grain average size. At the highest pressure (1.7 GPa), the minimum particle size (∼20 μm) turned out to be a more suitable quantity to describe the shock wave structure.

Detecting and characterizing the abundance and form of water-ice in permanently-shadowed regions of the moon using a three-band lidar system

We investigated the ability of a three-band lidar instrument (with wavelengths of 532, 1064, and 1560 nm) to detect and quantify different types of regolith ± water ice mixtures for both mare and highlands regions. A variety of samples were spectrally characterized, focusing on variables such as type of lunar regolith (simulant, lunar meteorite, highland vs mare), grain size (<45 μm, 45–1000 μm, <1 mm), water ice surface coverage and porosity of regolith (discontinuous, continuous, packed), and water ice percentages in intimate mixtures vs areal mixtures. Spectral metrics included absolute reflectance (532, 1064, 1560 nm) and reflectance ratios (1560/532, 1064/532, 1560/1064 nm). The ability to detect water ice in the presence of different types of regolith is critically dependent on the optical properties of end members, the selected wavelength, and the physical nature of the samples, such as grain size and areal vs intimate mixtures. Given the differences in the spectroscopic properties of the end members, both absolute reflectance and reflectance ratios have different predictive powers and both are required for robust analysis. The 1560 nm region is the most sensitive of the three wavelength regions to water ice content, as it falls well within a major water ice absorption band. Spectral contrast affects the ability to detect water ice. It is most sensitive for characterizing water ice + highland materials because the latter are brighter than water ice in this wavelength region. Powdered lunar materials are red-sloped across the 532 to 1064 to 1560 nm regions. By contrast, water ice shows a large downturn in reflectance between 1064 and 1560 nm. Detection limits for water ice in many situations can be as low as 2% and are lower for areal vs intimate mixtures. We found that porosity and angle of incidence with the surface have only minor effects on spectral reflectance properties of regolith. Further confirmation of water ice could be realized by comparing lidar data acquired by transects across permanently-shadowed regions and seeing how absolute reflectance and reflectance ratios vary between sunlit and adjacent shadowed regions. If it is known or assumed that regolith properties do not change as one enters a PSR, with the exception of the presence of surficial water ice, changes in reflectivity and reflectance ratios could provide compelling evidence for the presence of water ice.

Regolith of the Crater Floor Units, Jezero Crater, Mars: Textures, Composition, and Implications for Provenance

AbstractA multi‐instrument study of the regolith of Jezero crater floor units by the Perseverance rover has identified three types of regolith: fine‐grained, coarse‐grained, and mixed‐type. Mastcam‐Z, Wide Angle Topographic Sensor for Operations and eNgineering, and SuperCam Remote Micro Imager were used to characterize the regolith texture, particle size, and roundedness where possible. Mastcam‐Z multispectral and SuperCam laser‐induced breakdown spectroscopy data were used to constrain the composition of the regolith types. Fine‐grained regolith is found surrounding bedrock and boulders, comprising bedforms, and accumulating on top of rocks in erosional depressions. Spectral and chemical data show it is compositionally consistent with pyroxene and a ferric‐oxide phase. Coarse‐grained regolith consists of 1–2 mm well‐sorted gray grains that are found concentrated around the base of boulders and bedrock, and armoring bedforms. Its chemistry and spectra indicate it is olivine‐bearing, and its spatial distribution and roundedness indicate it has been transported, likely by saltation‐induced creep. Coarse grains share similarities with the olivine grains observed in the Séítah formation bedrock, making that unit a possible source for these grains. Mixed‐type regolith contains fine‐ and coarse‐grained regolith components and larger rock fragments. The rock fragments are texturally and spectrally similar to bedrock within the Máaz and Séítah formations, indicating origins by erosion from those units, although they could also be a lag deposit from erosion of an overlying unit. The fine‐ and coarse‐grained types are compared to their counterparts at other landing sites to inform global, regional, and local inputs to regolith formation within Jezero crater. The regolith characterization presented here informs the regolith sampling efforts underway by Perseverance.

Laboratory demonstration of space gamma-ray spectroscopy experiment with tags of Galactic cosmic rays for testing different types of Martian regolith

The laboratory demonstration of the space experiment was conducted at Joint Institute for Nuclear Research with a new type of planetary gamma-ray spectrometer (GRS-TCP) suite including a gamma-ray detector and a charged particle detector combined in coincidence mode. The proposed GRS prototype can select gamma-ray photons with time tags of charged particles of Galactic cosmic rays (GCR) from a predefined solid angle on the sky. It allows to collect gamma-rays only from a local spot on the irradiated surface under the rover or lander and rejects gamma-ray detections from the surrounding area/spacecraft body significantly improving signal-to-noise ratio. The main objective of this laboratory demonstration was to study the capability of this method to distinguish between local spots with different elemental compositions that could be passed by the rover along its traverse. For this purpose, the soil sample simulants corresponding to the different types of Martian regolith identified by Curiosity rover were created and tested by laboratory measurements. It was experimentally shown that our method of spectroscopy of gamma-rays with tags of charged particles could reliably detect local variations of the planetary regolith.

Soil-sample geochemistry normalised by class membership from machine-learnt clusters of satellite and geophysics data

The primary aim of mineral exploration is to focus the search space from regional scale (1000 s km2) to prospect scale (1–10 km2), identify areas that warrant further investigation, and ultimately drill a target. Mineral deposits typically display geochemical anomalism related to the conditions of their formation, or the weathering and mass transport of sediment away from a mineral deposit. However, this anomalism can be obscured in soil-sample surveys due to background variations in host bedrock chemistry and the transformation and redistribution of original minerals during surface weathering, regolith development, and supergene processes. This contribution uses machine-learnt map products to aid in the interpretation of a regional-scale soil-sample dataset. ASTER (satellite spectral) data were combined with airborne radiometric data using Self-Organising Maps (SOM) to generate a map of regolith type. A map of bedrock geology was previously derived by the authors from airborne geophysical data using Random Forests. These two products are used to classify soil samples with an objective bedrock-geology and regolith-type classification. A z-score normalisation was implemented on the soil-sample geochemical data, using two different matrices (regolith type and bedrock geology) to remove the bias of bedrock geology and regolith type from the soil sample chemistry. The signal that remains likely reflects metasomatic processes, and associated elemental anomalism, potentially linked to mineralisation. These data can then be plotted to provide maps of (pathfinder) element anomalies, thus identifying potential exploration targets. We explore this approach to normalise geochemical data in a dataset of 9,924 soil samples collected over an area of 1,028 km2, from Kerkasha, Eritrea (Nubian Shield). The Kerkasha project is an early-stage exploration project, with a limited understanding of the local geology and mineral deposit types; however, it contains many Au and Cu prospects that have received minimal exploration work.

Thermal emission measurements of ordinary chondrite mineral analogs in a simulated asteroid environment: 1. Constituent mineral phases

Telescopic surveys suggest that S-type asteroids are the dominant small body type in the near-Earth object population and are among the most abundant in the inner main asteroid belt. Given the link between S-type asteroids and the ordinary chondrites, regoliths of ordinary chondrite mineralogy may represent the most common regolith type on small bodies in these populations, and therefore it is important to understand the thermal emission properties of ordinary chondrite mineral analogs radiating into asteroid-like environments. Thermal infrared spectra of particulate surfaces in airless environments are substantially modified due to near-surface thermal gradients formed between the immediate surface undergoing radiative cooling and underlying materials that are warmed by the absorption of solar radiation. To advance our understanding of how the thermal emission properties of materials relevant to ordinary chondrite composition may be modified in an airless environment, we analyze a suite of analogous single mineral phases in a simulated asteroid surface environment. A companion paper presents and discusses analyses of modal mixtures of these minerals designed to match modal abundances of ordinary chondrites as reported in the literature. We probe the thermal emission of these materials by investigating relationships between their sample temperatures, emissivity spectra, brightness temperatures, and the environmental and experimental conditions. We focus attention on the radiance spectra of the samples as derived by two data reduction methods and their corresponding brightness temperature spectra to infer the intensity of near-surface thermal gradients formed in the samples. We demonstrate that the Christiansen feature position is sensitive to the sample cup temperature with data collected in a simulated asteroid environment under constant illumination condition. Through the analysis of particulate samples of three particle size ranges (<25 μm, 25–125 μm, and 125–250 μm) at ambient and cold, vacuum conditions, we demonstrate that thermal gradients form as a result of the physical, environmental, and optical properties of the target surface. Using temperature variations observed in high spectral resolution brightness temperature spectra as a proxy for the near-surface thermal gradients, we observe relationships between the intensity of the thermal gradient and the sample particle size. Modifications of iron metal spectra due to the changing environmental conditions are examined and compared with the silicate data. Implications for the measurement of thermal infrared spectra of metal-bearing planetary materials, such as the ordinary chondrites, are discussed.

Thermal emission measurements of ordinary chondrite mineral analogs in a simulated asteroid environment: 2. Representative mineral mixtures

We investigate a suite of synthetic mineral mixtures designed to act as bulk mineralogical analogs to H, L, and LL ordinary chondrite meteorites in order to probe how the thermal emission characteristics of such materials change between ambient and simulated asteroid environmental conditions. Due to the parent body link with certain S-type asteroids, studying these analog mixtures in an environment that is relevant to actual asteroid surfaces advances our understanding of the thermal emission properties of one of the most common regolith types among the main-belt and near-Earth asteroid populations. The observed changes in spectral emissivity features due to cold, vacuum conditions are not as large as previously observed for single mineral (silicate) samples. We interpret this difference to be the result of metallic and opaque components weakening near-surface thermal gradients in the mixtures. As such, we predict that near-surface thermal gradients on ordinary chondrite parent bodies (e.g., S-type asteroids) are likely much weaker than would be inferred from cold, vacuum measurements of individual mineral components. We tested whether the increased spectral contrast observed in fine-grained (<25 μm) samples measured in a cold, vacuum environment increases the efficacy of least squares linear unmixing methods. It is found that the accuracy of such models does not improve relative to measurements made under ambient conditions, thus linear unmixing models are not expected to yield accurate estimates of the modal mineralogy of airless planetary surfaces if they are dominated by fine-grained regolith. Mixtures with coarse particle sizes (125–250 μm) that were modeled using the coarse particle size endmembers yielded results that were largely independent of the environmental conditions, but with larger errors in spectral fits for samples measured in a simulated asteroid environment. At simulated asteroid environmental conditions, the bulk silicate composition and metal content play a more important role in determining the thermal state and brightness temperature of the sample than at ambient conditions. Modest changes in metal content (10–25 wt%) lead to large differences in the brightness temperature of a sample. Under simulated asteroid conditions, an ~10 K increase in maximum brightness temperature that tracks with increased iron content is observed at fine particle sizes (<25 μm) between each of the analog ordinary chondrite groups. Based on these results, it may be difficult to distinguish H, L, and LL compositions of suspected ordinary chondrite parent bodies using only Earth- or space-based thermal emission spectra. This is inferred from the spectral similarity of the analog mixtures and the absence of significant variation in spectral emissivity associated with reported differences in bulk metal content for ordinary chondrites.

Concentration-concentration fractal modelling: A novel insight for correlation between variables in response to changes in the underlying controlling geological-geochemical processes

Fractal/multifractal classification models applied to regional geochemical data are typically based on relationships between geochemical concentrations and mathematical, statistical or geometrical properties such as sample numbers, surface areas, perimeter and distance. There is, however, another component of geochemical datasets that is implicitly addressed using multi-variate methods such as factor analysis or various forms of clustering. This is the degree of correlation and changes in the nature of the correlation between elements as the processes affecting sample geochemistry change. In regional datasets, much of the change is related to differences in parent lithology or regolith type, but also relates to the effects of mineralisation or contamination. Where two elements display systematic changes in their mutual correlation in response to different ‘forcings’, joint modelling of such bivariate relationships can provide new ‘dimensions’ to data interpretation. Bivariate probability plots indicate distinct population breaks representing the intersections between different sub-populations within the two variables. This concept is extended in this study to fractal analysis and a proposed concentration-concentration (C–C) fractal model. A soil dataset from Cyprus was studied in this research to demonstrate and interpret the C–C results associated with copper (Cu)-related VMS mineralisation considering the geological-geochemical evidence. The C–C models generated based on the relation between Cu and indium (In) were compared to the established number-size (N-S), concentration-area (C-A), spectrum-area (S-A) and singularity models. All the models were applied to the same datasets, but in different formats, i.e., raw data, and multi-variate approaches of Box-Cox transformed data, factor analysis (FA) and centred log-ratio (clr) transformed data scores. This is to visualise and evaluate the robustness of the C–C model comparing to uni- and multi-variate studies. Therefore, based on the maps classified by the C–C model and the geology in Cyprus comparing to the mentioned models, the robustness of the C–C fractal model was demonstrated. In addition, applying Monte Carlo simulation on each class characterised by all the models applied, demonstrated a remarkably high certainty of the thresholds obtained by the C–C fractal model.

Can shallow groundwater sustain small-scale irrigated agriculture in sub-Saharan Africa? Evidence from N-W Ethiopia

We present an evidence-based approach to identify how best to support development of groundwater for small-scale irrigation in sub-Saharan Africa (SSA). We argue that it is important to focus this effort on shallow groundwater resources. We demonstrate and test this proposal at a case study site: Dangila woreda in the north-western highlands of Ethiopia. This site was selected to allow exploration of a shallow weathered volcanic regolith type aquifer formation which is found to the South of Lake Tana and also exists more extensively across Ethiopia. We believe lessons from this case study are transferable and there is a case for arguing that shallow groundwater represents a neglected opportunity for promoting sustainable small-scale irrigated agriculture in SSA.In comparison with other global regions, the groundwater resources of SSA are among the least understood; borehole records and hydrogeological studies are lacking. Assessments of groundwater resources do exist, but they rely on remotely sensed data combined with modelling at national or regional scale, and they focus on deeper aquifers. There is a need for these broad evaluations to be supplemented by localised and detailed assessments. The case study here presents such an assessment in order to support analysis of strengths, weaknesses, opportunities and threats associated with developing small-scale irrigation utilising shallow groundwater.A multimethod groundwater recharge assessment was conducted utilising formal and community-based monitoring, field investigation and existing published data. Water table recovery tests at existing hand dug wells confirm that well yields of 1 l/s are achievable at the end of the wet season when water would be available to support an additional irrigated crop. Hydraulic conductivity estimates ranged from 0.2 to 6.4 m/d in the dry season and from 2.8 to 22.3 m/day in the wet season. Specific yield estimations have a wider range though the mean value of 0.09 is as would be expected.Records of groundwater levels and rainfall monitored by the local community for the period April 2014 to April 2018 show that all the wells maintained useable water levels beyond the end of the rainy season. An assessment of the hydrology of the Kilti catchment provided insights into groundwater availability within the wider area. The catchment receives about 1600 mm/year of rainfall, of which about 350 mm/year enters the groundwater as recharge, discharging to the river as baseflow with a similar amount of rapid runoff contributing to a total river flow of about 400 mm/year. The lowest value of baseflow is 82% of the mean baseflow, which suggests a degree of buffering and indicates that groundwater is available even in a very dry year.We conclude that arguments previously put forward against the promotion of shallow groundwater use for agriculture in SSA appear exaggerated. Our analysis challenges the view that shallow aquifers are unproductive and that irrigation will have unacceptable impacts on wetlands and other groundwater-dependent ecosystems. We believe lessons from this case study are transferable, and there is a case for arguing that shallow groundwater represents a neglected opportunity for promoting sustainable small-scale irrigated agriculture in sub-Saharan Africa. It appears that factors other than the physical availability of groundwater control the ‘triggering’ of development. Interventions to promote development of groundwater resources should recognise the importance of shallow aquifers.

Targeting VHMS mineralization at Erayinia in the Eastern Goldfields Superterrane using lithogeochemistry, soil chemistry and HyLogger data

Exploration for volcanic-hosted massive sulfide (VHMS) deposits in the Archaean Yilgarn Craton of Western Australia is hampered by a combination of a paucity of outcrop, deep weathering, and saline groundwaters in geologically complex greenstone belts. We present a detailed account of the geology at Erayinia NW (Murrin Domain) in the southern part of the Kurnalpi Terrane, ~150 km SE of Kalgoorlie and 4 km NW of the King VHMS deposit (Edjudina Domain). We have used a combination of logging, petrography, lithogeochemical, pXRF, hyperspectral and soil datasets to help identify VHMS proximal signatures for future drill testing.Diamond drilling at Erayinia NW has identified widespread hydrothermal alteration and minor base metal mineralization across a strike length of at least 3 km. A lower package of calc-alkaline metabasalt, is overlain by intermediate volcanic and associated volcaniclastic rocks, a mixed sequence of argillaceous sedimentary rocks interbedded with FI to FII affinity dacitic rocks, and calc-alkaline metabasalt. SHRIMP UPb zircon geochronology has constrained the age of the host stratigraphy to 2685 ± 5 Ma. Hydrothermal alteration (quartz-sericite-pyrite) is most prevalent in the 50-75 m thick felsic dominated sequence interbedded with black shales, with local zones of chloritization associated with minor ZnPb mineralization. Massive pyrite was intercepted in the two southernmost holes located approximately 300 m apart.Black shales and hydrothermally altered felsic rocks contain elevated Ag, As, Bi, Cd, Cu, Hg, In, Mo, Pb, Sb, Te, Tl associated with increasing Zn concentrations. Broad halos of Sb, Tl, Eu/Eu* and normative corundum define the stratigraphy of interest. Hydrothermally altered felsic rocks are characterized by higher abundances of white mica and lesser chlorite than surrounding strata. Increased quantities of Mg-rich chlorite, muscovitic (Al-rich) white mica, and Fe‑carbonate (siderite) occur proximal to FeZn mineralization. Significant enrichments in trace elements (Ag, As, Bi, Cd, In, Mo, Ni, Sb, Sn, Te, Tl; plus Alteration Index and K2O; and lower Al, Ba, Sr) in black shales towards drillholes EC154D and EC157D suggest this area is most proximal to VHMS mineralization. Soil metal concentrations vary significantly according to underlying regolith type (e.g. colluvium, alluvium, playa lake). Geochemical data levelled by regolith type reveal several bulls-eye multi-element geochemical anomalies (e.g. Zn, Pb, Cu, As, Bi, Cd, Mo, Sn, Tl, W) over the King deposit (2.15 Mt. at 3.47 wt% Zn), King North occurrence (e.g. 1 m at 6.7 wt% Zn + Pb), with new targets identified at Erayinia NW and elsewhere for future drill testing.

Characterization of Regolith Types and its Impact on Gold Anomaly in Highly Weathered Terrains Using Multiple Dataset

Characterization of Regolith Types and its Impact on Gold Anomaly in Highly Weathered Terrains Using Multiple Dataset

Objective Regolith-Landform Mapping in a Regolith Dominated Terrain to Inform Mineral Exploration

An objective method for generating statistically sound objective regolith-landform maps using widely accessible digital topographic and geophysical data without requiring specific regional knowledge is demonstrated and has application as a first pass tool for mineral exploration in regolith dominated terrains. This method differs from traditional regolith-landform mapping methods in that it is not subject to interpretation and bias of the mapper. This study was undertaken in a location where mineral exploration has occurred for over 20 years and traditional regolith mapping had recently been completed using a standardized subjective methodology. An unsupervised classification was performed using a Digital Elevation Model, Topographic Position Index, and airborne gamma-ray radiometrics as data inputs resulting in 30 classes that were clustered to eight groups representing regolith types. The association between objective and traditional mapping classes was tested using the ‘Mapcurves’ algorithm to determine the ‘Goodness-of-Fit’, resulting in a mean score of 26.4% between methods. This Goodness-of-Fit indicates that this objective map may be used for initial mineral exploration in regolith dominated terrains.

Recognition of geochemical anomalies based on geographically weighted regression: A case study across the boundary areas of China and Mongolia

The identification of stream sediment geochemical anomalies related to mineralization from background is critically needed for mineral exploration using data processing method in the diverse lithological background and complex regolith terrains. In this research, a method based on geographically weighted regression (GWR) was presented for the identification of stream sediment geochemical anomalies. The concentrations of rock-forming oxides, lithophile elements, organic carbon and total carbon were taken as proxies for parent lithology and regolith type to adjust for variations in background of trace element geochemical patterns. Robust principal component analysis (RPCA) was conducted, and then the principal components were taken as spatially independent variables. The metallogenic elements were taken as dependent variables in GWR model, and the geochemical residuals were used to indicate local anomalies. The 1:1,000,000 stream sediment geochemical data across the boundary areas of China and Mongolia were analyzed, and the result of GWR was compared with that of a traditional method. It is found that the efficiency of GWR was highly improved compared with that of the traditional method, indicating that the proposed method can model and eliminate the background differences of elements due to lithological settings and landscapes. Anomalies identified by GWR had stronger spatial association with the known deposits, and thus can be used as guides to new exploration targets.

Porosity, permeability and compaction trends for Scandinavian regoliths

Abstract Weathered crystalline and metamorphic basement are proven as hydrocarbon reservoir rock in many areas of the world, including the Norwegian Continental Shelf. The reservoir properties of these rocks vary laterally and vertically as a function of the burial history, initial basement lithologies, sub-aerial exposure to weathering processes, chemical weathering, fault patterns, and these properties are relatively unknown. In this work, laboratory measurements are performed on different regolith types applying varying confining pressures representative for different degrees of basement weathering and burial depth. Porosity and permeability are measured on coherent samples (altered basement) and incoherent samples (disintegrated basement rock and saprolites) from the Utsira High (offshore Norway), and outcrop samples from Bomlo (southwestern Norway) and Ivo Klack (southern Sweden). Coherent samples from Utsira High (well 16/1-15 and 16/1-12) give porosities between 5.10% and 7.95% and permeabilities between 1.08 and 3.30 mD at 5.1 MPa, and indicate a relation between observed micro-fractures and decreasing permeabilities. In general, permeability increases with increasing amount of micro-fractures. The permeability is varying from 0.15 mD at 30 MPa to 3.30 mD at 5.1 MPa. This work presents the first published compaction curves for weathered basement (saprock and saprolites), and to our knowledge first permeability-porosity relationships for saprock and saprolites from three locations (Bomlo, Ivo Klack and Utsira High). The new porosity and permeability measurements of weathered basement rocks can be used as input parameters for reservoir modelling, basin modelling, field planning and hydrocarbon exploration in areas with regoliths. It can also serve as important input into hydrogeology, geothermal modelling, planning of tunnels, and as help to understand landslides and hillslope gullies in weathered basement.

Models of transport and reaction describing weathering of fractured rock with mobile and immobile water

We propose models for calculating the rate of chemical weathering of minerals as a function of depth in the weathering zone. A macropore network is assumed to be responsible for the transport of mobile water, which removes soluble weathering products at the interface of that network and the matrix. Conditions of infrequent rainfall (A) and of very frequent rainfall (B) are separately modeled, but both lead to a volumetric weathering rate with the general form , where the amplitude ν0 and the equilibration length ξ depend on the pore geometry of regolith and on parameters describing transport across the macropore‐matrix interface (A) or mineral dissolution (B). This is obtained with no assumption of steady state for regolith evolution. Extrapolating these end‐members into intermediate conditions, the model is consistent with the exponential decay of regolith production rate versus depth reported by several authors and yields ξ in a variety of regolith types in the range from centimeters to meters. The velocity of the regolith‐bedrock interface also shows an exponential decay with weathering zone thickness and is enhanced by bedrock fractures when compared to models of unfractured bedrock. When the residence time of fluid in the weathering zone, τf, is large, the bulk weathering rate Rb is inversely proportional to this time, and for small τf, Rb reverts to the laboratory rate. Application to compiled data from several sites leads to estimates of a dissolution rate constant and specific surface area consistent with those of albite.

A Preliminary Review of the Metallogenic Regularity of Nickel Deposits in China

AbstractThe nickel deposits mainly distributed in 19 provinces and autonomous regions in China are 339 ore deposits/occurrences, including 4 super large‐scale deposits, 14 large‐scale deposits, 26 middle‐scale deposits, 75 small‐scale deposits, and 220 mineralized occurrences. The prediction types of mineral resources of nickel deposits are magmatic type, marine sedimentary type and regolith type. The formation age is from the Neoarchean to the Cenozoic with two peaks in the Neoproterozoic and the late Paleozoic. The nickel deposits formed in the Neoproterozoic are located on the margin of the North China Block and Yangtze Block, and those formed in the late Paleozoic are mainly distributed in the Central Asian Orogenic Belt (CAOB), Emeishan and the Tarim Large Igneous Provinces (LIPs). Magmatic nickel deposits are mainly related with broken‐up continental margin, post‐collision extension of the orogenic belt and mantle plume. According to different tectonic backgrounds and main characteristics of magmatism, the Ni‐Cu‐Co‐PGE metallogenic series types of ore deposits related with mantle‐derived mafic‐ultramafic rocks can be divided into 4 subtypes: (1) the Ni‐Cu‐Co‐PGE metallogenic series subtype of ore deposits related with mantle‐derived mafic‐ultramafic rocks in the broken‐up continental margin, (2) the Ni‐Cu‐Co‐PGE metallogenic series subtype of ore deposits related with mantle‐derived mafic‐ultramafic rocks in mantle plume magmatism, (3) the Ni‐Cu‐Co‐PGE metallogenic series subtype of ore deposits related with mantle‐derived mafic‐ultramafic rocks in the subduction of the orogenic belt, and (4) the Ni‐Cu‐Co‐PGE metallogenic series subtype of ore deposits related with mantle‐derived mafic‐ultramafic rocks in post‐collision extension of the orogenic belt. We have discussed in this paper the typical characteristics and metallogenic models for Neoproterozoic Ni‐Cu‐(PGE) deposits related with broken‐up continental margin, Cambrian marine sedimentary Ni‐Mo‐V deposits related with black shale, early Permian Ni‐Cu deposits related with post‐collision extension of the orogenic belt, late Permian Ni‐Cu‐(PGE) deposits related with Large Igneous Provinces (LIPs), and Cenozoic Ni‐Au deposits related with regolith. The broken‐up continental margin, mantle plume and post‐collision extension of the orogenic belt are important ore‐forming geological backgrounds, and the discordogenic fault, mafic‐ultramafic intrusion, high MgO primitive magma (high‐MgO basaltic magma), deep magmatism, sulfur saturation and sulfide segregation are 6 important geological conditions for the magmatic nickel deposits.

A Preliminary Review of Metallogenic Regularity of Silver Deposits in China

China has widely distributed silver deposits, and is rich in silver resources. Although silver deposits are mainly associated with Pb‐Zn deposits, a number of independent silver deposits have also been discovered in recent years. Silver deposits include different types, such as submarine volcanism and continental volcanism related type, intrusion related type, and sedimentary related type. This study summarized the metallogenic regularity of China's silver deposits systematically based mainly on the data from 490 silver deposits. It is shown that submarine volcanic sedimentary type, continental volcanic or sub‐volcanic type, skarn type, hydrothermal type (including vein type and stratabound type), sedimentary metamorphic type, sedimentary type and regolith type should be regarded as the most important prediction types of silver deposit. A total of 32 silver mineralization belts and 111 silver concentration areas have been delineated. The map of “Spatial distribution of silver mineralization belts in China” and other series of maps finished in this study may provide a theoretical basis for the evaluation and prognosis of silver resources potential in China.